U.S. patent application number 14/696197 was filed with the patent office on 2015-11-19 for high voltage direct current transmission system and control method thereof.
This patent application is currently assigned to LSIS CO., LTD.. The applicant listed for this patent is LSIS CO., LTD.. Invention is credited to Ho Hwan PARK, Gum Tae SON.
Application Number | 20150333648 14/696197 |
Document ID | / |
Family ID | 53054872 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150333648 |
Kind Code |
A1 |
SON; Gum Tae ; et
al. |
November 19, 2015 |
HIGH VOLTAGE DIRECT CURRENT TRANSMISSION SYSTEM AND CONTROL METHOD
THEREOF
Abstract
A high voltage direct current (HVDC) transmission system is
provided. The high voltage direct current (HVDC) transmission
system includes a rectifier converting alternating current (AC)
power into DC power; an inverter converting the DC power into the
AC power; DC transmission lines W1 and W2 transmitting the DC power
obtained from the rectifier through conversion to the inverter; a
first active power measurement unit measuring first active power
input to the rectifier; a second active power measurement unit
measuring second active power output from the inverter; and a first
control unit controlling the operations of the rectifier and the
inverter based on the first active power measured and the second
active power measured, wherein the first control unit senses
oscillation generated in the HVDC transmission system and generates
a control signal for damping the sensed oscillation to control one
or more of the rectifier and the inverter.
Inventors: |
SON; Gum Tae; (Seoul,
KR) ; PARK; Ho Hwan; (Suwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LSIS CO., LTD. |
Anyang-si |
|
KR |
|
|
Assignee: |
LSIS CO., LTD.
Anyang-si
KR
|
Family ID: |
53054872 |
Appl. No.: |
14/696197 |
Filed: |
April 24, 2015 |
Current U.S.
Class: |
363/35 |
Current CPC
Class: |
Y02E 60/60 20130101;
H02J 2003/365 20130101; H02J 3/36 20130101; H02M 7/7575 20130101;
H02M 5/40 20130101; H02M 5/458 20130101; H02M 1/12 20130101 |
International
Class: |
H02M 5/44 20060101
H02M005/44; H02M 1/12 20060101 H02M001/12 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2014 |
KR |
10-2014-0058029 |
Claims
1. A high voltage direct current (HVDC) transmission system
comprising: a rectifier converting alternating current (AC) power
into DC power; an inverter converting the DC power into the AC
power; DC transmission lines W1 and W2 transmitting the DC power
obtained from the rectifier through conversion to the inverter; a
first active power measurement unit measuring first active power
input to the rectifier; a second active power measurement unit
measuring second active power output from the inverter; and a first
control unit controlling the operations of the rectifier and the
inverter based on the first active power measured and the second
active power measured, wherein the first control unit senses
oscillation generated in the HVDC transmission system and generates
a control signal for damping the sensed oscillation to control one
or more of the rectifier and the inverter.
2. The high voltage direct current (HVDC) transmission system
according to claim 1, wherein the first control unit comprises: an
oscillation sensing unit sensing oscillation generated in the HVDC
transmission system; a damping control unit generating the control
signal for damping the generated oscillation based on the sensed
oscillation; and a signal output unit transmitting the generated
control signal.
3. The high voltage direct current (HVDC) transmission system
according to claim 1, wherein the damping control unit comprises: a
first damping control unit generating an active power control
signal controlling active power in generating the control signal,
and a second damping control unit generating a reactive power
control signal controlling reactive power in generating the control
signal.
4. The high voltage direct current (HVDC) transmission system
according to claim 3, wherein the damping control unit generates
the control signal based one or more of the active power control
signal and the reactive power control signal.
5. The high voltage direct current (HVDC) transmission system
according to claim 1, wherein the first control unit determines
whether the frequency of the sensed oscillation is within a preset
range, and generates the control signal for damping the sensed
oscillation when as a result of determination, the frequency of the
sensed oscillation is within the preset range.
6. The high voltage direct current (HVDC) transmission system
according to claim 1, wherein the first active power measurement
unit measures an AC current and an AC voltage input to the
rectifier to measure the first active power, and the second active
power measurement unit measures an AC current and an AC voltage
output from the inverter to measure the second active power.
7. The high voltage direct current (HVDC) transmission system
according to claim 1, further comprising a second control unit
receiving the second active power measured by the second active
power measurement unit.
8. The high voltage direct current (HVDC) transmission system
according to claim 1, further comprising: a first AC filter
removing a harmonic current generated in the power conversion
process of the rectifier, and a second AC filter removing the
harmonic current generated in the power conversion process of the
inverter.
9. The high voltage direct current (HVDC) transmission system
according to claim 1, wherein each of the rectifier and the
inverter comprises any one of a thyristor value and an insulated
gate bipolar transistor (IGBT) valve.
10. The high voltage direct current (HVDC) transmission system
according to claim 1, further comprising: a first capacitor
connected in parallel to the rectifier and smoothing a DC voltage
output from the rectifier; and a second capacitor connected in
parallel to the inverter and smoothing a DC voltage input to the
inverter.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. .sctn.119(a), this application claims
the benefit of earlier filing date and right of priority to Korean
Patent Application No. 10-2014-0058029, filed on May 14, 2014, the
contents of which are all hereby incorporated by reference herein
in its entirety.
BACKGROUND
[0002] The present disclosure relates to a high voltage direct
current (HVDC) transmission system, and more particularly, to an
HVDC transmission system that may damp oscillation generated in the
HVDC transmission system, and a control method thereof.
[0003] High voltage direct current (HVDC) transmission indicates a
power transmission method of converting, by a transmission site, AC
power produced at a power station into DC power to transmit the DC
power and then re-converting, by a reception site, AC power into DC
to supply AC power.
[0004] An HVDC system is applied to submarine cable power
transmission, large-amount long-distance power transmission,
interconnection between AC systems, etc. Also, the HVDC
transmission system enables different frequency system
interconnection and asynchronism interconnection.
[0005] The transmission site converts the AC power into the DC
power. That is, since transmitting the AC power by using a
submarine cable is significantly dangerous, the transmission site
converts the AC power into the DC power to transmit the DC power to
the reception site.
[0006] The HVDC transmission system may have mechanical, torsional
oscillation according to the operation of a three-phase AC
generator in the HVDC system.
[0007] When the low-frequency oscillation including the mechanical,
torsional oscillation is maintained or amplified without
disappearing in the HVDC, it may have a serious effect on the
stability of a power system in the HVDC system.
[0008] Thus, there is a need to damp low-frequency oscillation
generated in the HVDC transmission system.
SUMMARY
[0009] Embodiments provide a high voltage direct current (HVDC)
transmission system that may sense the low-frequency oscillation in
the HVDC system and damp the sensed low-frequency oscillation, and
a control method thereof.
[0010] In one embodiment, a high voltage direct current (HVDC)
transmission system includes a rectifier converting alternating
current (AC) power into DC power; an inverter converting the DC
power into the AC power; DC transmission lines W1 and W2
transmitting the DC power obtained from the rectifier through
conversion to the inverter; a first active power measurement unit
measuring first active power input to the rectifier; a second
active power measurement unit measuring second active power output
from the inverter; and a first control unit controlling the
operations of the rectifier and the inverter based on the first
active power measured and the second active power measured, wherein
the first control unit senses oscillation generated in the HVDC
transmission system and generates a control signal for damping the
sensed oscillation to control one or more of the rectifier and the
inverter.
[0011] The first control unit include: an oscillation sensing unit
sensing oscillation generated in the HVDC transmission system; a
damping control unit generating the control signal for damping the
generated oscillation based on the sensed oscillation; and a signal
output unit transmitting the generated control signal.
[0012] The damping control unit may include: a first damping
control unit generating an active power control signal controlling
active power in generating the control signal, and a second damping
control unit generating a reactive power control signal controlling
reactive power in generating the control signal.
[0013] The damping control unit may generate the control signal
based one or more of the active power control signal and the
reactive power control signal.
[0014] The first control unit may determine whether the frequency
of the sensed oscillation is within a preset range, and generates
the control signal for damping the sensed oscillation when as a
result of determination, the frequency of the sensed oscillation is
within the preset range.
[0015] The first active power measurement unit may measure an AC
current and an AC voltage input to the rectifier to measure the
first active power, and the second active power measurement unit
measures an AC current and an AC voltage output from the inverter
to measure the second active power.
[0016] The high voltage direct current (HVDC) transmission system
may further include a second control unit receiving the second
active power measured by the second active power measurement
unit.
[0017] The high voltage direct current (HVDC) transmission system
may further include: a first AC filter removing a harmonic current
generated in the power conversion process of the rectifier, and a
second AC filter removing the harmonic current generated in the
power conversion process of the inverter.
[0018] Each of the rectifier and the inverter may include any one
of a thyristor value and an insulated gate bipolar transistor
(IGBT) valve.
[0019] The high voltage direct current (HVDC) transmission system
may further may include: a first capacitor connected in parallel to
the rectifier and smoothing a DC voltage output from the rectifier;
and a second capacitor connected in parallel to the inverter and
smoothing a DC voltage input to the inverter.
[0020] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features
will be apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram for explaining the configuration of a
high voltage direct current (HVDC) transmission system according to
an embodiment.
[0022] FIG. 2 is a diagram for explaining the actual configuration
of an HVDC transmission system according to an embodiment.
[0023] FIG. 3 is a block diagram of the control unit of an HVDC
transmission system according to an embodiment.
[0024] FIG. 4 is a block diagram of the control unit of an HVDC
transmission system according to another embodiment.
[0025] FIG. 5 is a flowchart of a control method of an HVDC
transmission system according to an embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0026] Some embodiments are described below in more detail with
reference to the accompanying drawings. Since the suffixes "module"
and "unit" for components used in the following description are
given and interchanged for easiness in making the present
disclosure, they do not have distinct meanings or functions.
[0027] The effects and features of the inventive concept, and
implementation methods thereof will be clarified through following
embodiments below described in detail with reference to the
accompanying drawings. An embodiment may, however, be embodied in
different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided to make this disclosure thorough and complete and fully
convey the scope of an embodiment to a person skilled in the art.
Further, the inventive concept is only defined by scopes of claims.
Like reference numerals throughout the disclosure refer to like
components.
[0028] When describing embodiments, detailed descriptions related
to known functions or configurations will be ruled out in order not
to unnecessarily obscure subject matters of the embodiments. In
addition, since the terms used herein are defined in consideration
of functions in the embodiments, they may vary depending on a
user's or operator's intention or practice. Therefore, their
definitions need to be made based on details throughout the present
disclosure.
[0029] Combinations of each block of the accompanying drawing and
combinations of each step of a flowchart may also be performed by
computer program instructions. Since the computer program
instructions may be loaded on the processor of a general-purpose
computer, a special-purpose computer or other programmable data
processing equipment, the instructions performed by the processor
of the computer or other programmable data processing equipment
create a means that performs functions described on each block of a
drawing or each step of a flowchart. Since the computer program
instructions may also be stored in a computer usable or computer
readable memory that may aim at the computer or other programmable
data processing equipment in order to implement functions in a
specific manner, the instructions stored in the computer usable or
computer readable memory may also produce an item that includes an
instruction means performing functions described on each block of a
drawing or each step of a flowchart. The computer program
instructions may also be loaded on the computer or other
programmable data processing equipment. Thus, since a series of
operation steps are performed on the computer or other programmable
data processing equipment to create processes executed by a
computer, instructions operating the computer or other programmable
data processing equipment may also provide steps for performing
functions described on each block of a drawing and each step of a
flowchart.
[0030] Also, each block or each step may represent a portion of a
module, a segment or a code that includes one or more executable
instructions for performing specific logical function(s). Also, it
should be noted that some alternatives may be performed in such a
way that functions mentioned at blocks or steps are performed in a
different order. For example, two blocks or steps shown one after
another may also be performed substantially at the same time or the
blocks or steps may also be sometimes performed in a reverse order
according to a corresponding function.
[0031] FIG. 1 is a diagram for explaining the configuration of a
high voltage direct current (HVDC) transmission system according to
an embodiment.
[0032] An HVDC transmission system 1 according to an embodiment may
be any one of a thyristor-based HVDC transmission system and a
voltage-based HVDC system. The thyristor-based HVDC system may be a
current-based HVDC transmission system using a thyristor valve as a
rectifier, and the voltage-based HVDC transmission system may be a
system using an insulated gate bipolar transistor (IGBT)
device.
[0033] In the case of the thyristor-based HVDC system, a rotation
device, such as a generator or synchronous compensator in order to
rectify a thyristor valve is needed for an inverter-side system,
and a capacitor bank for compensating for reactive power may be
included in the rectifier or the inverter-side system.
[0034] Since the voltage-based HVDC system significantly decreases
harmonics through fast switching, it is possible to decrease the
size of a harmonic filter for removing the harmonics and there is
no need to supply reactive power. Also, the voltage-based HVDC
transmission system may independently control active power and
reactive power.
[0035] Referring to FIG. 1, the HVDC transmission system 1
according to an embodiment includes a first power converter 10 and
a second power converter 20.
[0036] The first power converter 10 includes an AC power supply
device 11, a first transformer 12, a rectifier 13, a cooler 14, and
a first control unit 15.
[0037] The AC power supply device 11 may produce AC power and
transmit the AC power to the first transformer 12. In an
embodiment, the AC power supply device 11 may be a power station
that may produce and supply power, such as a wind power
station.
[0038] The first transformer 12 may increase the size of the AC
voltage of the AC power received from the AC power supply device 11
and convert it to AC power having a high voltage.
[0039] The rectifier 13 may convert HVAC power converted from the
first transformer 12 into DC power.
[0040] The cooler 14 may cool heat emitting from the rectifier 13.
In particular, the cooler 14 may cool heat emitting from the
rectifier 13 and related parts, by circulating coolant.
[0041] The first control unit 15 may control the overall operations
of the first power converter 10.
[0042] In particular, the first control unit 15 may control the
size of AC power, the phase of AC power, active power and reactive
power of any one terminal of the first power converter 10.
[0043] The first control unit 15 may sense oscillation generated in
the HVDC transmission system 1, generate a control signal capable
of damping low-frequency oscillation based on the sensed
oscillation, and control the operation of the first power converter
10 based on the generated control signal.
[0044] The DC power converted through the rectifier 13 may be
transmitted to the second power converter 20 through a DC line.
[0045] The second power converter 20 includes an inverter 21, a
second transformer 22, an AC power supply device 23, a cooler 24,
and a second control unit 25.
[0046] The inverter 21 converts the DC power received from the
first power converter 10 through the DC line, into AC power.
[0047] The second transformer 22 converts the AC power obtained
through conversion from the inverter 21, into low voltage AC
power.
[0048] The AC power supply device 23 receives the low voltage AC
power from the second transformer 22.
[0049] The cooler 24 may cool heat emitting from the inverter
21.
[0050] The second control unit 25 controls the overall components
of the second converter 20.
[0051] In particular, the second control unit 25 may control the
size of AC power, the phase of AC power, active power and reactive
power of any one terminal of the first power converter 20.
[0052] Also, the second control unit 25 may sense oscillation
generated in the HVDC transmission system 1, generate a control
signal capable of damping low-frequency oscillation based on the
sensed oscillation, and control the operation of the second power
converter 20 based on the generated control signal.
[0053] FIG. 2 is a diagram for explaining the actual configuration
of an HVDC transmission system according to an embodiment.
[0054] Referring to FIG. 2, the HVDC transmission system 1
according to an embodiment includes the first power converter 10
and the second power converter 20.
[0055] The first power converter 10 may convert AC power into DC
power to provide the DC power to the second power converter 20, and
the second power converter 20 may convert the DC power received
from the first power converter 10 into AC power.
[0056] The first power converter 10 and the second power converter
20 may be connected by positive-pole DC transmission lines W1 and
W2. The DC transmission lines W1 and W2 may transmit a DC current
or a DC voltage output by the first power converter 10 to the
second power converter 20.
[0057] The DC transmission lines W1 and W2 may be any one of an
overhead line and a cable, or a combination thereof.
[0058] The first power converter 10 includes an AC power supply
device 11, a first AC filter 16, a first inductor 17, a rectifier
13, a first capacitor C1, a first measurement unit Ml, a second
measurement unit M3, a third measurement unit M7, and a first
control unit 15.
[0059] The AC power supply device 11 may produce AC power and
transmit the AC power to the rectifier 13. The AC power supply
device 11 may be a power station that may produce and supply power,
such as a wind power station.
[0060] The AC power supply device 11 may transmit three-phase AC
power to the rectifier 13.
[0061] The first AC filter 16 may be disposed between the AC power
supply device 11 and the rectifier 13. The first AC filter 16 may
remove current harmonics generated in the process of converting AC
power into DC power by the rectifier 13. That is, the first AC
filter 16 may remove the current harmonics to block the current
harmonics from entering the AC power supply device 11. In an
embodiment, the first AC filter 16 may include a resonant circuit
including a capacitor, an inductor, and a resistor.
[0062] Also, the first AC filter 16 may also supply reactive power
consumed in the rectifier 13.
[0063] The first inductor 17 may be disposed between the first AC
filter 13 and the rectifier 13.
[0064] The first inductor 17 may transmit, to the rectifier 13, an
AC current from which the current harmonics have been removed
through the first AC filter 16.
[0065] The first inductor 17 may be an inductor that adjusts the
phase of the AC current from which the current harmonics have been
removed through the first AC filter 16.
[0066] The rectifier 13 may convert the AC power received from the
AC power supply device 11, in particular, from the first inductor
17, into DC power.
[0067] The rectifier 13 may be a semiconductor valve that may
convert AC power into DC power. In an embodiment, the semiconductor
valve may be any one of a thyristor valve and an IGBT valve.
[0068] The first capacitor C1 may be a smoothing capacitor that is
connected in parallel to the rectifier 13 and smoothes a DC voltage
output from the rectifier 13.
[0069] The first measurement unit M1 may measure an AC voltage UL1
supplied by the AC power supply device 11 and transmit a measured
voltage to the first control unit 15.
[0070] The first measurement unit M1 may measure an AC voltage UL1
of a point between the AC power supply device 11 and the first AC
filter 16 and transmit a measured voltage to the first control unit
15. In the following, the AC voltage UL1 measured on the point
between the AC power supply device 11 and the first AC filter 16 is
referred to as a bus voltage UL1.
[0071] The second measurement unit M3 may measure an AC current IV1
or AC voltage UV1 input to the output of the first inductor 17 or
to the rectifier 13 and transmit a measured current or voltage to
the first control unit 15. In the following, the AC voltage UV1
input to the output of the first inductor 17 or to the rectifier 13
is referred as a bridge voltage UV1.
[0072] The third measurement unit M7 may measure a DC voltage Ud1
across the first capacitor C1 and transmit a measured voltage to
the first control unit 15.
[0073] The first control unit 15 may control the overall operations
of the first power converter 10.
[0074] The first control unit 15 may control the operations of the
rectifier 13 based on the bus voltage UL1 received from the first
measurement unit M1, the AC current IV1 received from the second
measurement unit M3 and input to the rectifier 13, and the DC
voltage Ud1 received from the third measurement unit M7 and across
the first capacitor C1.
[0075] When the rectifier 13 is of an IGBT valve type, the first
control unit 15 may transmit a turn-on signal or turn-off signal to
the rectifier 13 based on the bus voltage UL1 received from the
first measurement unit M1, the AC current IV1 received from the
second measurement unit M3 and input to the rectifier 13, and the
DC voltage Ud1 received from the third measurement unit M7 and
across the first capacitor C1 to control the operations of the
rectifier 13. The conversion from AC power into DC power may be
controlled by the turn-on signal or turn-off signal.
[0076] Also, the first control unit 15 may generate a phase change
command signal based on an abnormal voltage state on the DC
transmission lines W1 and W2, and adjust the phase difference
between the bridge voltage UV1 and the bus voltage UL1 according to
the generated phase change command signal.
[0077] In particular, when a DC voltage (e.g., the DC voltage Ud1
across the first capacitor C1) measured at a point on the DC
transmission line W1 exceeds a reference value for a certain time,
the first control unit 15 may confirm that there is an abnormal
voltage on the DC transmission line.
[0078] When it is confirmed that there is the abnormal voltage on
the DC transmission line, the first control unit 15 may generate a
phase change command signal and adjust the phase difference between
the bridge voltage UV1 and the bus voltage UL1.
[0079] The first control unit 15 may adjust the phase difference
between the bridge voltage UV1 and the bus voltage UL1 to adjust a
DC voltage obtained through conversion from the rectifier 13, so it
is possible to prevent a DC voltage on the DC transmission line
from sharply increasing.
[0080] Also, the first control unit 15 may sense oscillation
generated in the HVDC transmission system 1, generate a control
signal capable of damping low-frequency oscillation based on the
sensed oscillation, and control the operation of the first power
converter 10 based on the generated control signal.
[0081] In particular, the operation of damping low-frequency
oscillation of the first control unit 15 is described with
reference to FIG. 3.
[0082] Referring to FIG. 3, the first control unit 15 includes an
oscillation sensing unit 10, a damping control unit 130, and a
signal output unit 150.
[0083] The oscillation sensing unit 110 may sense oscillation
generated in the HVDC transmission system 1.
[0084] Since the oscillation sensing unit 110 includes a sensor
capable of sensing oscillation, it is possible to sense oscillation
generated in the HVDC transmission system 1 and it is possible to
measure the frequency of sensed oscillation.
[0085] The damping control unit 130 may generate a control signal
capable of damping low-frequency oscillation based on the sensed
oscillation.
[0086] In particular, the damping control unit 130 may determine
whether the frequency of the sensed oscillation is within a preset
range, and generate a control signal capable of damping
low-frequency oscillation based on the sensed oscillation when as a
result of determination, the frequency of the sensed oscillation is
within the preset range.
[0087] In addition, the control signal may include an active power
control signal controlling active power and a reactive power
control signal controlling reactive power.
[0088] Referring to FIG. 4, the damping control unit 130 may
include a first damping control unit 131 and a second damping
control unit 132.
[0089] The first damping control unit 131 may generate an active
power control signal controlling active power in generating the
control signal.
[0090] The second damping control unit 132 may generate a reactive
power control signal controlling reactive power in generating the
control signal.
[0091] Thus, since the damping control unit 130 may generate the
active power control signal through the first damping control unit
131 and the reactive power control signal through the second
damping control unit 132, it is possible to control the operation
of the first power converter 10 based on one or more of the
generated active power control signal and the generated reactive
power control signal.
[0092] Refer back to FIG. 3.
[0093] The signal output unit 150 may transmit the generated
control signal to each of associated devices.
[0094] In particular, the signal output unit 150 may transmit the
control signal generated by the damping control unit 130 to one or
more of associated devices including the AC power supply device 11,
the first transformer 12, the rectifier 13, and the cooler 14 so
that each device may operate.
[0095] Also, the signal output unit 150 may also convert the
generated control signal to transmit a converted signal to each of
associated devices.
[0096] For example, the signal output unit 150 may convert the
control signal in order to be suitable for each of the associated
devices including the AC power supply device 11, the first
transformer 12, the rectifier 13 and the cooler 14, and transmit a
converted signal to each device.
[0097] Refer back to FIG. 2.
[0098] The second power converter 20 includes an inverter 21, a
second capacitor C2, a second inductor 27, a second AC filter 26,
an AC power supply device 23, a fourth measurement unit M8, a fifth
measurement unit M6, a sixth measurement unit M4, and a second
control unit 25.
[0099] The inverter 21 may be a semiconductor valve that may
convert DC power received from the rectifier 13, into AC power. In
an embodiment, the semiconductor valve may be any one of a
thyristor valve and an IGBT valve.
[0100] The inverter 21 may receive a DC current or a DC voltage
from the inverter 21 through the DC transmission lines W1 and W2,
and converter the received DC current or DC voltage into an AC
current or an AC voltage.
[0101] The second capacitor C2 may be connected in parallel to the
inverter 21, and may be a smoothing capacitor that smoothes the DC
voltage input to the inverter 21.
[0102] The second inductor 27 may be disposed between the inverter
21 and the second AC filter 26. The second inductor 27 may transmit
the AC current output from the inverter 21, to the AC power supply
device 23. The second inductor 27 may be a phase inductor that
adjusts the phase of an AC current.
[0103] The second AC filter 26 may be disposed between the second
inductor 27 and the AC power supply device 23. The second AC filter
26 may remove current harmonics generated in the process of
converting DC power into AC power by the inverter 21. That is, the
second AC filter 26 may remove the current harmonics to block the
current harmonics from entering the AC power supply device 23. In
an embodiment, the second AC filter 26 may include a resonant
circuit including a capacitor, an inductor, and a resistor.
[0104] Also, the second AC filter 26 may also supply reactive power
consumed in the inverter 21.
[0105] The AC power supply device 23 may receive, through the
second AC filter 26, AC power from which the harmonics have been
removed.
[0106] The fourth measurement unit M8 may measure a DC voltage Ud2
across the second capacitor C2 and transmit a measured voltage to
the second control unit 25.
[0107] The fifth measurement unit M6 may measure an AC current IV2
or AC voltage UV2 output from the input of the second inductor 27
or from the inverter 21 and transmit a measured current or voltage
to the second control unit 25. In the following, the AC voltage UV2
output from the output of the second inductor 27 or from the
inverter 21 is referred as a bridge voltage UV2.
[0108] The sixth measurement unit M4 may measure an AC voltage UL2
supplied by the AC power supply device 23 and transmit a measured
voltage to the second control unit 25. The sixth measurement unit
M4 may measure the AC voltage UL2 of a point between the AC power
supply device 23 and the second AC filter 26 and transmit a
measured voltage to the second control unit 25. In the following,
the AC voltage UL2 measured on the point between the AC power
supply device 23 and the second AC filter 26 is referred to as a
bus voltage UL2.
[0109] The second control unit 25 may control the overall
operations of the second power converter 20.
[0110] The second control unit 25 may control the operations of the
inverter 21 based on the bus voltage UL2 received from the sixth
measurement unit M4, the AC current IV2 received from the fifth
measurement unit M6 and output from the inverter 21, and the DC
voltage Ud2 received from the sixth measurement unit M4 and across
the second capacitor C2.
[0111] If the inverter 21 is of an IGBT valve type, the second
control unit 25 may transmit a turn-on signal or turn-off signal to
the inverter 21 based on the bus voltage UL2 received from the
sixth measurement unit M4, the AC current IV2 received from the
fifth measurement unit M6 and output from the inverter 21, and the
DC voltage Ud2 received from the fourth measurement unit M8 and
across the second capacitor C2 to control the operations of the
inverter 21. The conversion from DC power into AC power may be
controlled by the turn-on signal or turn-off signal.
[0112] Also, the second control unit 25 may generate a phase change
command signal based on an abnormal voltage state on the DC
transmission lines W1 and W2, and adjust the phase difference
between the bridge voltage UV2 and the bus voltage UL2 according to
the generated phase change command signal.
[0113] In particular, when a DC voltage (e.g., the DC voltage Ud2
across the second capacitor C2) measured at a point on the DC
transmission line W1 exceeds a reference value for a certain time,
the second control unit 25 may confirm that there is an abnormal
voltage on the DC transmission line. When it is confirmed that
there is the abnormal voltage on the DC transmission line, the
second control unit 25 may generate a phase change command signal
and adjust the phase difference between the bridge voltage UV2 and
the bus voltage UL2.
[0114] Also, the second control unit 25 may sense oscillation
generated in the HVDC transmission system 1, generate a control
signal capable of damping low-frequency oscillation based on the
sensed oscillation, and control the operation of the second power
converter 20 based on the generated control signal.
[0115] In particular, the operation of damping low-frequency
oscillation of the second control unit 25 is described with
reference to FIG. 3.
[0116] Referring to FIG. 3, the second control unit 25 includes an
oscillation sensing unit 110, a damping control unit 130, and a
signal output unit 150.
[0117] The oscillation sensing unit 110 may sense oscillation
generated in the HVDC transmission system 1.
[0118] Since the oscillation sensing unit 110 includes a sensor
capable of sensing oscillation, it is possible to sense oscillation
generated in the HVDC transmission system 1 and it is possible to
measure the frequency of sensed oscillation.
[0119] The damping control unit 130 may generate a control signal
capable of damping low-frequency oscillation based on the sensed
oscillation.
[0120] In particular, the damping control unit 130 may determine
whether the frequency of the sensed oscillation is within a preset
range, and generate a control signal capable of damping
low-frequency oscillation based on the sensed oscillation when as a
result of determination, the frequency of the sensed oscillation is
within the preset range.
[0121] In addition, the control signal may include an active power
control signal controlling active power and a reactive power
control signal controlling reactive power.
[0122] Referring to FIG. 4, the damping control unit 130 may
include a first damping control unit 131 and a second damping
control unit 132.
[0123] The first damping control unit 131 may generate an active
power control signal controlling active power in generating the
control signal.
[0124] The second damping control unit 132 may generate a reactive
power control signal controlling reactive power in generating the
control signal.
[0125] Thus, since the damping control unit 130 may generate the
active power control signal through the first damping control unit
131 and the reactive power control signal through the second
damping control unit 132, it is possible to control the operation
of the second power converter 20 based on one or more of the
generated active power control signal and the generated reactive
power control signal.
[0126] Refer back to FIG. 3.
[0127] The signal output unit 150 may transmit the generated
control signal to each of associated devices.
[0128] In particular, the signal output unit 150 may transmit the
control signal generated by the damping control unit 130 to one or
more of associated devices including the AC power supply device 23,
the first transformer 23, the rectifier 21, and the cooler 24 so
that each device may operate.
[0129] Also, the signal output unit 150 may also convert the
generated control signal to transmit a converted signal to each
device.
[0130] For example, the signal output unit 150 may convert the
control signal in order to be suitable for each of the associated
devices including the AC power supply device 23, the second
transformer 22, the inverter 21 and the cooler 24, and transmit a
converted signal to each device.
[0131] The operation method of an HVDC transmission system
according to an embodiment is described with reference to FIG.
5.
[0132] FIG. 5 is a flowchart of a control method of an HVDC
transmission system according to an embodiment.
[0133] In the following, the control method of the HVDC
transmission system according to an embodiment is described in
conjunctions with FIGS. 1 to 4.
[0134] Firstly, the control method of the first power converter 10
is described.
[0135] The oscillation sensing unit 110 of the first control unit
15 senses oscillation generated in the HVDC transmission system 1
in step S110.
[0136] The oscillation sensing unit 110 may sense oscillation
generated in the HVDC transmission system 1 and measure the
frequency of the sensed oscillation.
[0137] For example, the oscillation sensing unit 110 may sense
mechanical, torsional oscillation generated in an AC generator in
the AC power supply device 11.
[0138] The oscillation sensing unit 110 may transmit information on
the sensed oscillation to the damping control unit 130.
[0139] The damping control unit 130 of the first control unit 15
determines whether the sensed oscillation is within a preset range
in step S130.
[0140] The damping control unit 130 may determine whether the
frequency of the sensed oscillation is within a preset range.
[0141] For example, when the frequency of the sensed oscillation is
within a preset range of about 0.1 Hz to about 2.0 Hz, the damping
control unit 130 may determine that the sensed oscillation is
low-frequency oscillation. In this example, the preset range from
about 0.1 Hz to about 2.0 Hz is provided for description and a
preset range may be set variously according to a user's or
designer's choice.
[0142] The damping control unit 130 of the first control unit 15
generates a control signal based on the sensed oscillation, when
the sensed oscillation is within the preset range in step S150. The
damping control unit 130 may generate a control signal capable of
damping low-frequency oscillation based on the sensed oscillation,
when as a result of determination in step S130, the sensed
oscillation is within the preset range.
[0143] In particular, the damping control unit 130 may generate one
or more of an active power control signal and a reactive power
control signal capable of damping low-frequency oscillation based
on the sensed oscillation.
[0144] Thus, the first damping control unit 131 may generate the
active power control signal controlling active power based on the
sensed oscillation, and the second damping control unit 132 may
generate the reactive power control signal controlling reactive
power based on the sensed oscillation.
[0145] The control signal generated by the damping control unit 130
may be transmitted to the signal output unit 150.
[0146] The signal output unit 150 of the first control unit 15
operates associated devices based on the generated control signal
in step S170.
[0147] The signal output unit 150 may transmit the generated
control signal to one or more of associated devices including the
AC power supply device 11, the first transformer 12, the rectifier
13, and the cooler 14 so that each device may operate.
[0148] For example, the signal output unit 150 may convert the
control signal in order to be suitable for each of the associated
devices including the AC power supply device 11, the first
transformer 12, the rectifier 13 and the cooler 14, and transmit a
converted signal to each device.
[0149] Thus, each of the devices receiving the control signal may
operate based on the control signal capable of damping
low-frequency oscillation.
[0150] Therefore, it is possible to damp low-frequency oscillation
generated in the HVDC transmission system 1.
[0151] Subsequently, the control method of the second power
converter 20 is described.
[0152] The oscillation sensing unit 110 of the second control unit
25 senses oscillation generated in the HVDC transmission system 1
in step S110.
[0153] The oscillation sensing unit 110 may sense oscillation
generated in the HVDC transmission system 1 and measure the
frequency of the sensed oscillation.
[0154] For example, the oscillation sensing unit 110 may sense
mechanical, torsional oscillation generated in an AC generator in
the AC power supply device 23.
[0155] The oscillation sensing unit 110 may transmit information on
the sensed oscillation to the damping control unit 130.
[0156] The damping control unit 130 of the second control unit 25
determines whether the sensed oscillation is within a preset range
in step S130.
[0157] The damping control unit 130 may determine whether the
frequency of the sensed oscillation is within the preset range.
[0158] For example, when the frequency of the sensed oscillation is
within a preset range of about 0.1 Hz to about 2.0 Hz, the damping
control unit 130 may determine that the sensed oscillation is
low-frequency oscillation. In this example, the preset range from
about 0.1 Hz to about 2.0 Hz is provided for description and a
preset range may be set variously according to a user's or
designer's choice.
[0159] The damping control unit 130 of the second control unit 25
generates a control signal based on the sensed oscillation, when
the sensed oscillation is within the preset range in step S150.
[0160] The damping control unit 130 may generate a control signal
capable of damping low-frequency oscillation based on the sensed
oscillation, when as a result of determination in step S130, the
sensed oscillation is within the preset range.
[0161] In particular, the damping control unit 130 may generate one
or more of an active power control signal and a reactive power
control signal capable of damping low-frequency oscillation based
on the sensed oscillation.
[0162] Thus, the first damping control unit 131 may generate the
active power control signal controlling active power based on the
sensed oscillation, and the second damping control unit 132 may
generate the reactive power control signal controlling reactive
power based on the sensed oscillation.
[0163] The control signal generated by the damping control unit 130
may be transmitted to the signal output unit 150.
[0164] The signal output unit 150 of the second control unit 25
operates associated devices based on the generated control signal
in step S170.
[0165] The signal output unit 150 may transmit the generated
control signal to one or more of associated devices including the
AC power supply device 11, the first transformer 12, the rectifier
13, and the cooler 14 so that each device may operate.
[0166] For example, the signal output unit 150 may convert the
control signal in order to be suitable for each of the associated
devices including the AC power supply device 23, the second
transformer 22, the inverter 21 and the cooler 24, and transmit a
converted signal to each device.
[0167] Thus, each of the devices receiving the control signal may
operate based on the control signal capable of damping
low-frequency oscillation.
[0168] Therefore, it is possible to damp low-frequency oscillation
generated in the HVDC transmission system 1.
[0169] According to the control method of the HVDC transmission
system according to embodiments, it is possible to damp
low-frequency oscillation generated in the HVDC transmission system
1.
[0170] According to embodiments, since it is possible to damp
low-frequency oscillation based on a reactive power control signal,
an active power transmission operation may not be obstructed.
[0171] According to an embodiment, the above-described method may
also be embodied as processor readable codes on a program-recorded
medium. Examples of the processor readable medium are a ROM, a RAM,
a CD-ROM, a magnetic tape, a floppy disk, an optical data storage
device, and a carrier wave form (such as data transmission through
the Internet).
[0172] The above-described embodiments are not limited to the
above-described configuration and method, and some or all of the
embodiments may also be selectively combined so that various
variations may be implemented.
[0173] Also, although exemplary embodiments have been illustrated
and described above, the inventive concept is not limited to
specific embodiments described above but may be varied by a person
skilled in the art without departing from the subject matter of the
inventive concept claimed in the following claims and the
variations should not be understood separately from the technical
spirit or perspective of the inventive concept.
* * * * *